Conventionally, an airbag is provided to improve safety in vehicle collision. As to the airbag, a technique for changing airbag control at vehicle collision according to occupant type such as adult and child has been proposed (see Patent Document 1).
Patent Document 1: JP 2004-53324A (corresponding to US 2004/0021305A)
The inventor of the present application has found that there is the following difficulty in typical airbag control. In the typical airbag control, after detection of impact on the vehicle, pressure inside the airbag increases with time and reaches its maximum pressure after a while, and thereafter decreases with time. In the above, if a distance “d” between the driver's face and the steering wheel is small, the driver's face may collide with the steering wheel before the airbag is sufficiently inflated. Additionally, if the distance “d” is large, the pressure of the airbag has already decreased below the maximum pressure at a time when the driver's face collides with the steering wheel.